It's a case worthy of a Sherlock Holmes story. The mystery over the death of a British spy has only deepened this week as new details emerged this week at the official inquest into how he died.

The naked body of Gareth Williams, 31, was found curled up inside a locked duffle bag in the bathtub of his London apartment on Aug. 16, 2010. Scotland Yard has so far failed to solve the case in an investigation that has lasted nearly two years.

At the time of his death, Williams was working as a codebreaker at Britain's Secret Intelligence Service, or SIS, also known as MI6.

Police investigators told the inquest that there was no indication of a break-in at the apartment, and nothing to suggest that evidence at the scene was destroyed.

Williams' body showed no signs of struggle, nor that Williams had been drugged or poisoned. Detective Chief Inspector Jackie Sebire said police had been working under the assumption that Williams could not have entered and locked the duffle bag by himself, and that a third party must have been involved. Sebire revealed Tuesday that "two minor components of another contributor's DNA" were found on the bag's zip toggle and padlock.

Williams' family said it believed that another person must have been involved in his death.

Also found at the dead man's apartment was a newspaper cutting of an article about the regrets commonly held by terminally ill patients in the last weeks of their lives. Headlined "Top Five Regrets of the Dying," the story was about a book of the same name written by an Australian nurse who'd spent several years working in palliative care and recorded the dying epiphanies of her patients. The regrets included "I wish I'd had the courage to live a life true to myself, not the life others expected of me;" "I wish I hadn't worked so hard;" "I wish I'd had the courage to express my feelings."

Closed-circuit TV images of Williams visiting luxury stores in West London in the days before he died do not suggest he was being followed. Police said thousands of dollars worth of women's designer clothes were found at Williams' apartment, as well as wigs and makeup. Asked whether Williams was a transvestite, an old friend told the inquest that she did not believe so, and said the items were likely purchased as gifts.

It's not clear why it took a week for detectives to visit the apartment after the codebreaker failed to show up to work at the headquarters of Britain's intelligence service on Aug. 16.

Williams was working at SIS after he was transferred to the agency by Britain's Government Communications Headquarters, its secret electronic surveillance agency, where he had previously been employed. In April 2010, he successfully applied to return to GCHQ earlier than planned.